The present disclosure relates generally to toners and toner processes, and more specifically, to toner compositions having triboelectric charging properties tailored to enhance the compatibility of pigment(s) utilized therewith and combinations thereof.
Numerous processes are known for the preparation of toners, such as, for example, conventional processes wherein a resin is melt kneaded or extruded with a pigment, micronized and pulverized to provide toner particles. In addition, there are illustrated in U.S. Pat. Nos. 5,364,729 and 5,403,693, the disclosures of each of which are hereby incorporated by reference in their entirety, methods of preparing toner particles by blending together latexes with pigment particles. Also relevant are U.S. Pat. Nos. 4,996,127, 4,797,339 and 4,983,488, the disclosures of each of which are hereby incorporated by reference in their entirety.
Toner can also be produced by emulsion aggregation methods. Methods of preparing an emulsion aggregation (EA) type toner are known and toners may be formed by aggregating a colorant with a latex polymer formed by emulsion polymerization. For example, U.S. Pat. No. 5,853,943, the disclosure of which is hereby incorporated by reference in its entirety, is directed to a semi-continuous emulsion polymerization process for preparing a latex by first forming a seed polymer. In particular, the '943 patent describes a process including: (i) conducting a pre-reaction monomer emulsification which includes emulsification of the polymerization reagents of monomers, chain transfer agent, a disulfonate surfactant or surfactants, and optionally, but in embodiments, an initiator, wherein the emulsification is accomplished at a low temperature of, for example, from about 5° C. to about 40° C.; (ii) preparing a seed particle latex by aqueous emulsion polymerization of a mixture including (a) part of the monomer emulsion, from about 0.5 to about 50 percent by weight, or from about 3 to about 25 percent by weight, of the monomer emulsion prepared in (i), and (b) a free radical Initiator, from about 0.5 to about 100 percent by weight, or from about 3 to about 100 percent by weight, of the total initiator used to prepare the latex polymer at a temperature of from about 35° C. to about 125° C., wherein the reaction of the free radical initiator and monomer produces the seed latex comprised of latex resin wherein the particles are stabilized by surfactants; (iii) heating and feed adding to the formed seed particles the remaining monomer emulsion, from about 50 to about 99.5 percent by weight, or from about 75 to about 97 percent by weight, of the monomer emulsion prepared In (ii), and optionally a free radical initiator, from about 0 to about 99.5 percent by weight, or from about 0 to about 97 percent by weight, of the total Initiator used to prepare the latex polymer at a temperature from about 35° C. to about 125° C.; and (iv) retaining the above contents in the reactor at a temperature of from about 35° C. to about 125° C. for an effective time period to form the latex polymer, for example from about 0.5 to about 8 hours, or from about 1.5 to about 6 hours, followed by cooling. Other examples of emulsion/aggregation/coalescing processes for the preparation of toners are illustrated in U.S. Pat. Nos. 5,290,654, 5,278,020, 5,308,734, 5,370,963, 5,344,738, 5,403,693, 5,418,108, 5,364,729, and 5,346,797, the disclosures of each of which are hereby incorporated by reference in their entirety. Other processes are disclosed in U.S. Pat. Nos. 5,348,832, 5,405,728, 5,366,841, 5,496,676, 5,527,658, 5,585,215, 5,650,255, 5,650,256 and 5,501,935, the disclosures of each of which are hereby incorporated by reference in their entirety.
Color toners are within the purview of those skilled in the art. In U.S. Pat. Nos. 5,556,727, 5,591,552, 5,554,471, 5,607,804, and 5,620,820, the disclosures of each of which are hereby incorporated by reference in their entirety, there is illustrated a combination of four color toners for the development of electrostatic latent images enabling the formation of a full color gamut image, wherein the four toners include a cyan toner, a magenta toner, a yellow toner, and a black toner. Each of these toners include a resin and pigment, wherein the pigment for the cyan toner is a β-copper phthalocyanine, the pigment for the magenta toner is a xanthene silicomolybdic acid salt of RHODAMINE 6G basic dye, the pigment for the yellow toner is a diazo benzidine, and the pigment for the black toner is carbon black.
In U.S. Pat. No. 5,688,626, the disclosure of which is hereby incorporated by reference in its entirety, a gamut toner aggregation process is disclosed including a process for the preparation of a combination of color toners including a cyan toner, a magenta toner, a yellow toner, and a black toner. Each of these toners include a resin and pigment, wherein the pigment is cyan, magenta, yellow and black, and each of the pigments are dispersed in a nonionic, or neutral charge surfactant.
Toner systems normally fall into two classes: two component systems, in which the developer material includes magnetic carrier granules having toner particles adhering triboelectrically thereto; and single component systems, which typically use only toner. The operating latitude of a powder xerographic development system may be determined to a great degree by the ease with which toner particles may be supplied to an electrostatic image. Placing charge on the particles, to enable movement and development of images via electric fields, is most often accomplished with triboelectricity. Triboelectric charging may occur either by mixing the toner with larger carrier beads in a two component development system or by rubbing the toner between a blade and donor roll in a single component system.
Triboelectricity may be unpredictable because of the sensitivity of the materials utilized in forming toner. For example, for toners made by conventional methods, the grinding process may result in exposed pigments, which may act as charge control agents causing the different color toners to behave different with respect to triboelectric properties. This difference, in turn, may lead to a high degree of incompatibility between the primary color toners which may be used to form the foundation of new colors by dry blending. The sensitivity of the toner materials may also cause difficulties in identifying a triboelectrically compatible set of color toners that can be blended for custom colors.
To enable “offset” print quality with powder-based electrophotographic development systems, small toner particles (about 5 micron diameter) may be desired. Although the functionality of small, triboelectrically charged toner has been demonstrated, concerns remain regarding the long-term stability and reliability of such systems.
Development systems which use triboelectricity to charge toner, whether they be two component (toner and carrier) or single component (toner only), tend to exhibit nonuniform distribution of charges on the surfaces of the toner particles. This nonuniform charge distribution may result in high electrostatic adhesion because of localized high surface charge densities on the particles. For example, the electrostatic adhesion forces for tribo-charged toner, which are dominated by charged regions on the particle at or near its points of contact with a surface, do not rapidly decrease with decreasing size. This so-called “charge patch” effect makes smaller, triboelectric charged particles much more difficult to develop and control. Toner adhesion, especially in the development step, can limit performance by hindering toner release.
Moreover, if one attempts to blend different color parent toners under the same blend conditions, the charging properties of the colors may be dominated by pigment effects leading to different charging, and therefore incompatibility. Often, the charging effects caused by pigments are compensated by additional charge control agents which cause the different colors to diverge in additive formulations, which also leads to incompatibility for dry blending.
Improved methods for producing toner, which increase the compatibility of different color toners thereby reducing the cost associated with such toners, and which are capable of utilizing existing processing equipment and machinery, remain desirable.